JP4440682B2 - Vibrating gyro - Google Patents

Description

  The present invention relates to a vibrating gyroscope that detects angular velocity.

  Conventionally, a mechanical rotary gyroscope has been used as an inertial navigation device for airplanes and ships, but the device is large and expensive, so it is difficult to incorporate it into a small electronic device or a small transport machine.

  In recent years, however, research on miniaturization of gyroscopes has progressed, and a vibrating body is excited by a piezoelectric element, and a voltage generated by vibration caused by Coriolis force that the vibrating body receives by rotation is detected by another piezoelectric element provided on the vibrating body. Vibrating gyros have been put into practical use and are used in automobile navigation systems and video camera shake detection devices.

  In particular, a vibrating gyroscope using a piezoelectric single crystal has a simple structure, is easy to adjust, and has excellent temperature characteristics, and is considered promising. As an example using a piezoelectric single crystal, the structure of a tuning fork type vibration gyro using quartz will be described below with reference to the drawings. FIG. 5 is a perspective view showing a tuning fork type vibration gyro. FIG. 6 is a cross-sectional view and a schematic diagram of a drive detection circuit for explaining a drive detection method of a conventional tuning fork type crystal gyro.

  5 and 6, the tuning fork J10 has a structure in which a drive detection electrode is vapor-deposited on an integrally processed quartz crystal. That is, the tuning fork J10 has a structure in which the first leg J11 and the second leg J12 arranged in parallel are coupled to the base J15. Drive electrodes J1, J2, J3, and J4 are deposited on the first leg J11, and four detection electrodes J5, J6, J7, and J8 are formed along the four corners on the second leg J12. Vapor deposited. The bottom surface of the base J15 is used for support. Here, the extending direction of the legs is defined as the Y ′ direction, the direction in which the two legs are arranged is defined as the X direction, and the direction orthogonal to the X and Y ′ directions is defined as the Z ′ direction.

  The operation will be described. In FIG. 6, the cross sections of the drive electrodes J1, J2, J3 and J4 are arranged on the cross section of the first leg J11 shown on the left side, and the detection electrodes J5, J6 and J6 are shown on the cross section of the second leg J12 shown on the right side. Cross sections of J7 and J8 are arranged.

  First, when the first leg J11 is bent in the X direction toward the second leg J12, for example, the vicinity of the electrode J2 extends in the Y ′ direction and the vicinity of the electrode J4 contracts in the Y ′ direction. Due to the effect, an electric field is generated in the X direction in the vicinity of the electrode J2, and in the -X direction in the vicinity of the electrode J4. At this time, considering the direction of the electric field, the electrodes J2 and J4 have the same potential, for example, a higher potential than the center of the leg. When viewed in the X direction, the electrodes J1 and J3 arranged near the center of the leg J11 have a relatively lower potential than the electrodes J2 and J4, and therefore, between the electrodes J2 and J4 and the electrodes J1 and J3, A potential difference occurs. Since the piezoelectric effect is reversible, if a potential difference is applied between the electrodes J2 and J4 and the electrodes J1 and J3, an electric field corresponding to this is generated inside the crystal, and the first leg J11 bends in the X direction. It will be. From these things, for example, the potential of the electrodes J1 and J3 is used as a reference to amplify with the amplifier JG at an amplification factor exceeding the oscillation condition, and adjusted to a phase satisfying the oscillation condition by the phase shift circuit JP and returned to the electrodes J2 and J4. As a result, energy exchange occurs between the mechanical return force and the electrical force accompanying the bending of the first leg J11, and the first leg J11 can oscillate in the X direction.

Looking at the tuning fork J10 as a whole, when the first leg J11 moves in the X direction to balance the momentum of the first leg J11 and the second leg J12, the second leg J12 moves in the -X direction, 1 leg J
When 11 moves in the -X direction, the second leg J12 moves in the X direction. This is because the conventional tuning fork vibrates in one plane. Although called, the vibration generated by the first leg J11, the amplifier JG and the phase shift circuit JP is the same operation as the in-plane bending vibration, and its frequency substantially matches the resonance frequency of the in-plane bending vibration of the tuning fork J10.

When the entire tuning fork J10 is rotated around the Y ′ axis at an angular velocity Ω in this state, the Coriolis force Fc acts on the two legs of the tuning fork J10 in the Z ′ direction perpendicular to the in-plane bending vibration. The Coriolis force FC can be expressed by the following equation.
FC = 2 ・ M ・ Ω ・ V
Here, M is the mass of the first leg J11 or the second leg J12, and V is the speed of the first leg J11 or the second leg J12. This Coriolis force FC excites the first leg J11 and the second leg J12 to bend vibrations that are displaced in the Z ′ direction perpendicular to the X direction, which is the operation direction of in-plane bending vibrations. Hereinafter, this is referred to as out-of-plane bending vibration. Further, since the Coriolis force is not a displacement but a force proportional to the velocity, the out-of-plane bending vibration generated by the Coriolis force is generated with a phase delay of 90 degrees from the in-plane bending vibration.

  By this out-of-plane bending vibration, for example, the vicinity of the electrodes J5 and J8 of the second leg J12 expands and contracts in the Y 'direction, and the vicinity of the electrodes J6 and J7 expands and contracts in a phase opposite to that of the vicinity of the electrodes J5 and J8. For example, when the vicinity of the electrodes J5 and J8 extends in the Y ′ direction, an electric field is generated in the X direction in the vicinity of the electrodes J5 and J8 inside the second leg J12. At this time, in the vicinity of the electrodes J6 and J7 Is contracted in the Y ′ direction, an electric field is generated in the −X direction in the vicinity of the electrodes J6 and J7 inside the second leg 12. That is, when the potential of the electrode J5 is higher than the potential of the electrode J8, the potential of the electrode J7 is higher than the potential of the electrode J6. When the vicinity of the electrodes J5 and J8 is contracted in the Y ′ direction, an electric field is generated in the −X direction in the vicinity of the electrodes J5 and J8 inside the second leg J12. At this time, the electrodes J6 and J7 Since the vicinity extends in the Y ′ direction, an electric field is generated in the X direction in the vicinity of the electrodes J6 and J7 inside the second leg 12. That is, when the potential of the electrode J5 is lower than the potential of the electrode J8, the potential of the electrode J7 is lower than the potential of the electrode J6.

  The potential difference between the electrodes J5 and J8 and the electrodes J6 and J7 generated by the out-of-plane bending vibration changes according to the direction of the second leg J12 that swings in the Z ′ direction. In other words, for example, when the electrode J5 is at a high potential, the electrode J7 is also at a high potential. At this time, the electrodes J6 and J8 are at a low potential, and when the electrode J5 is at a low potential, the electrode J7 is also at a low potential. The hour electrode J6 and the electrode J8 are at a high potential. The Coriolis force appears as a potential difference between the electrode J5 or the electrode J7 and the electrode J6 or the electrode J8.

  The detection signal of the Coriolis force is guided to the multiplication circuit JM through the differential buffer JD with the electrodes J5 and J7 as one input signal and the electrodes J6 and J8 as the other input signal, and the in-plane bending vibration is detected. The output of the amplifier JG is shifted by 90 degrees by the phase shift circuit JP2 and multiplied by the reference signal binarized by the comparator JC for the purpose of correcting the generation of the Coriolis force delayed by 90 degrees. The result detected by multiplication is further smoothed by the integrating circuit JS and can be detected as an accurate DC output. Since this DC output is proportional to the Coriolis force FC, and the Coriolis force FC is proportional to the angular velocity Ω, the angular velocity Ω can be known from this DC output (see Non-Patent Document 1).

On the other hand, Patent Document 1 shows that the performance of a vibrating gyroscope can be improved by adopting an asymmetric three-leg tuning fork shape in which one leg of a three-leg tuning fork vibrator having three legs is stationary. ing.
Japanese Patent Laid-Open No. 2003-156337 (FIG. 1, FIG. 2, pages 2 to 7) T. T. IEEE Japan, Vol. 118-E, no. 7/8, '98 (P377-P383)

  However, the tuning fork type vibration gyro using a conventional crystal has the following problems. Among the factors that determine the output of a vibrating gyroscope, the degree of detuning defined by the difference between the frequency of the drive vibration and the detected vibration is inversely proportional to the output of the gyro, and the slight change in it greatly changes the output of the gyro. However, with current crystal processing accuracy, this detuning degree is within the range where temperature characteristics are not degraded or pseudo output against vibration is not produced, and the desired output is produced with a larger value. It is difficult to set the value within the range of the target setting value that can fully demonstrate

  If only the frequency is adjusted, it can be adjusted after processing with a frequency adjustment method that changes the mass of the tip used for general oscillator tuning forks, but the resonance frequency on both the drive side and the detection side is almost the same amount. Therefore, it is difficult to adjust the degree of detuning with this adjustment method.

  An object of the present invention is to solve the above-described problems, and provides a vibration gyro in which a change in detection output is gentle with respect to a change in detuning degree.

In order to solve the above object, the vibration gyro of the present invention employs the following configuration. A vibrator having three legs arranged at the base, an oscillating means for driving two of the three legs at a predetermined drive frequency, and another one different from the driven two legs Detecting means for detecting the Coriolis force by the legs of the three legs, the three legs being arranged in parallel in the same direction from the base with a predetermined distance from each other, and the oscillating means of the three legs Among them, the center leg and one leg adjacent to the center leg are driven, the other leg adjacent to the center leg is substantially stationary, and the detection means generates the Coriolis force generated on the other leg. In the vibration gyro to detect, the vibrator has a first detection vibration mode with a first vibration frequency as a resonance point, and a second detection vibration mode with a second vibration frequency as a resonance point, The drive frequency of the oscillating means is between the first vibration frequency and the second vibration frequency. Characterized in that it is a frequency.
Further, the first detection vibration mode vibration and the second detection vibration mode vibration generated based on the Coriolis force act so that the other leg vibrates in the same phase.
Further, the first detection vibration mode is a mode in which the one leg and the other leg vibrate in an opposite phase to the center leg, and the second detection vibration mode is the one leg and the center leg. The leg is in a mode that vibrates in an opposite phase to the other leg.
The width of the other leg is narrower than the width of the central leg and the width of the one leg.
In addition, the width of the one leg and the width of the central leg are made substantially the same, and the width of the other leg is 3/5 ± 10% of the width of the one leg or the central leg. And a shoulder is provided at a portion connecting the one leg and the base.

  The vibration gyro according to the present invention has a plurality of detected vibrations. For example, in a three-leg tuning fork type vibration gyro, the drive vibration frequency is set between two detection vibration frequencies that are regions in which the detection output hardly changes by adjusting the degree of detuning. By doing so, it is possible to realize a stable output characteristic in which the detection output hardly changes depending on the degree of detuning.

  The best mode for carrying out the present invention will be described below with reference to examples.

  Hereinafter, an embodiment according to the best mode for carrying out a vibrating gyroscope of the present invention will be described with reference to the drawings. 1 to 4 and FIGS. 7 to 9 show a vibrating gyroscope according to an embodiment of the present invention. FIG. 1 shows an appearance of a three-leg tuning fork type vibrating gyro, which will be referred to as a three-leg tuning fork 10 hereinafter. 2 is a cross-sectional view of a tripod tuning fork 10, a circuit block, and a schematic wiring diagram. FIG. 3 shows the appearance of a three-leg tuning fork type vibrating gyroscope, shows the coordinates, FIG. 4 is a front view showing a part, FIG. 4 is a rear view showing the appearance of a tripod tuning fork type vibration gyro, showing coordinates, and part of an electrode, and FIGS. FIG. 10 is a diagram for explaining an operation of a leg cross section showing a vibration mode of the body, and FIG. 10 is a diagram illustrating an output of a three-leg tuning fork type vibration gyro with respect to frequency.

[Structural description of vibrating gyroscope: FIGS. 1 to 4]
In the present embodiment, a crystal having excellent temperature characteristics is used among the piezoelectric single crystals. Crystal is a Si0 ₂ single crystal at normal temperature belongs to trigonal system with four crystal axes. One of the crystal axes is called the c-axis and is the crystal axis passing through the apex of the crystal, and the other three are called the a-axis and are crystal axes that form an angle of 120 degrees with each other in a plane perpendicular to the c-axis. It is. Here, one of the three a-axes is taken as the X-axis, the c-axis is taken as the Z-axis, and the Y-axis is taken in a direction perpendicular to the X-axis and the Z-axis.

  As shown in FIG. 1, the coordinate system used in the present embodiment is a coordinate axis Y′-axis rotated from the X, Y, and Z axes around the X axis by θ degrees in the direction from the Z axis to the Y axis. , Z ′ axis and X axis are used. At this time, the rotation angle θ is set to 0 to 10 degrees. The rotation angle shown here is selected optimally using the temperature characteristics and the stability of vibration as indices. The tripod tuning fork 10 has a two-dimensional shape with a constant thickness, and is cut out with this thickness direction as the Z′-axis direction. The tripod tuning fork shape of the tripod tuning fork 10 cut out in this way is expressed in a two-dimensional shape in the X-Y ′ plane. Here, in the following description, the Z′-axis direction is the front and back direction, the surface orthogonal to the Z ′ axis viewed from the Z ′ direction is referred to as the front surface, and the surface orthogonal to the Z ′ axis viewed from the −Z ′ direction is referred to as the back surface. The X-axis direction is the left-right direction, the plane orthogonal to the X-axis viewed from the X direction is referred to as the left side, and the plane orthogonal to the X-axis viewed from the -X direction is referred to as the right side.

  FIG. 1 is a view of the tripod tuning fork 10 viewed from an oblique direction, but the electrodes are omitted. As shown in FIG. 1, the three-leg tuning fork 10 includes legs 1 to 3, a base portion 9 and a support portion 11. The leg 1 is made of a quartz crystal having elasticity and piezoelectricity, and the shape is a rectangular column having the same length, the length L in the Y ′ direction, the width W1 in the X direction, and the thickness t in the Z ′ direction. And an electrode made of a metal vapor deposition film provided on the side surface. The legs 2 are made of quartz having elasticity and piezoelectricity, and the shape is a rectangular column having a length L in the Y ′ direction, a width W2 in the X direction, and a thickness t in the Z ′ direction. It has an electrode made of a deposited film. The legs 3 are made of quartz having elasticity and piezoelectricity, and the shape thereof is a rectangular column having a length L in the Y ′ direction, a width W3 in the X direction, and a thickness t in the Z ′ direction. It has an electrode made of a deposited film. Here, the ratio W1: W2: W3 of the widths of the legs 1, 2 and 3 is approximately 5: 5: 3. The base 9 is made of a quartz crystal having elasticity, and the shape thereof is a rectangular column having a length D in the Y ′ direction, a width W1 + W2 + W3 + 2 × U + K in the X direction, and a thickness t in the Z ′ direction. The support part 11 is made of a quartz crystal having elasticity, and the shape thereof is a quadrangular column whose width in the X direction is 1/3 to 1/1 of the width of the base part and whose thickness in the Z ′ direction is t. The legs 1 to 3 are arranged in parallel with each other in the order of leg 1, leg 2 and leg 3 in the X direction, with a gap U therebetween, and each leg is joined to one surface perpendicular to the Y ′ direction of the base 9. ing. At this time, the left side surface of the base portion 9 and the left side surface of the leg 1 are not a single plane, and the leg 1 is disposed inward in the X direction from the side surface of the base portion 9 by K and a left shoulder portion is formed. Further, the right side surface of the base portion 9 and the right side surface of the leg 3 are arranged to be a single plane, and the right shoulder portion is not formed. The support portion 11 is joined to the center of another surface called a bottom surface that is parallel to the joined surfaces of the legs 1 to 3 of the base portion 9. All the above parts have the same thickness, are in the same plane, and are monolithic.

3 and 4 show a state in which an electrode made of a metal vapor deposition film is formed on a tripod tuning fork 10 as an example of the electrode. However, the support part 11 which is not related to the description of the electrodes is omitted. FIG. 3 shows the tripod tuning fork 10 viewed from the Z ′ direction. FIG. 4 shows the tripod tuning fork 10 as viewed from the −Z ′ direction. As already described, the surface shown in FIG. 3 is called the front surface, and the surface shown in FIG. 4 is called the back surface. The shape of the electrode is formed by preparing a mask having a shape created by etching in advance, and bringing the mask into close contact with the front and back surfaces on which the electrode of the tripod tuning fork 10 is formed, and performing vacuum deposition. The left and right side electrodes can be formed by rotating the deposition direction. Electrode 1U is deposited on the surface of leg 1, electrode 1D on the back surface, electrode 1L on the left side, electrode 1R on the right side, electrode 2U on the surface of leg 2, electrode 2D on the back side, electrode 2L on the left side, electrode 2L on the right side. Electrode 2R is vapor-deposited, electrode 3U which goes around from the surface of leg 3 to the right side, electrode 3D which goes around from the back to the right side, and electrode 3G is vapor-deposited on the left side. All electrodes are rectangular. On the surface of the base portion 9, terminals DR, SE, S1, S2 and GND for connecting to the circuit and conductive wires connecting the electrodes and the terminals of the respective legs are deposited.

  FIG. 2 shows the same legs 1 to 3 as shown in FIGS. 3 and 4, and the electrodes 1L, 1R, 1U, 1D, 2L, 2R, 2U, 2D, 3U, 3D and 3G in the Y′-axis direction. A vertical section is shown, and the connection relation of each electrode and the drive detection circuit are shown. The drive circuit includes a self-oscillation circuit that returns signals from the detection electrodes 1L, 1R, 2U, and 2D to the drive electrodes 1U, 1D, 2L, and 2R using the amplifier G and the phase shift circuit P. The differential buffer D that detects signals from the detection electrodes 3U and 3D, the phase shift circuit P2 that changes the phase of the output of the amplifier G, the comparator C that binarizes the signal of the phase detection circuit, and the output of the differential buffer D A multiplication circuit M that multiplies the output of the phase shift circuit P2 and an integration circuit S that integrates the multiplication result into a direct current. In the case of a three-power supply circuit, the electrode 3G that is not directly connected to the drive detection circuit is grounded.

[Description of Operation and Action of Vibration Gyro: FIGS. 2 and 7 to 10]
Hereinafter, the detected vibration of the tripod tuning fork type vibrating body will be described with reference to FIGS. 7 and 9, the driving vibration of the tripod tuning fork type vibrating body will be described with reference to FIG. 8, and obtained with two detected vibrations in FIG. 10. The tendency of the output will be described. Finally, a method of electrically driving the tripod tuning fork 10 and knowing the angular velocity from the voltage output resulting from the rotation of the tripod tuning fork 10 will be described with reference to FIG.

  First, the fact that the coordinate system for cutting out the tripod tuning fork 10 used in the present embodiment is tilted from the crystal axis of the crystal will be described. The quartz used in this embodiment is an anisotropic single crystal, and the temperature dependence of the elastic modulus differs depending on the direction. The thickness direction is not the Z-axis direction, and the coordinate direction Y′-axis, Z′-axis, and X-axis rotated around the X-axis by θ degrees from the Z-axis to the Y-axis are used. This is because the temperature characteristic of the resonance frequency of the drive detection vibration varies depending on the rotation angle θ, so that the rotation angle θ is determined in consideration of the temperature characteristic. The rotation angle θ is selected from 0 to 10 degrees in consideration of the temperature condition in which the vibrating gyroscope is used.

In the vibration gyro, it is effective in that the detection unit does not generate an output unrelated to the Coriolis force while driving vibration is generated in order to suppress high S / N and troublesome output drift during no rotation. is there. This is because there is no drift if there is no output during no rotation. If the orthogonality between the drive and detection vibrations is incomplete, the output unrelated to the Coriolis force will cause the drive vibration to mechanically generate the detection vibration in the vibrating detection section, and if the electrode symmetry is incomplete. In the detection unit that vibrates, the drive output electrically generates the detection output. Therefore, the vibration body manufactured with finite machining accuracy is detected regardless of the drive vibration when the drive vibration is generated when there is no rotation. It is desirable that the part is stationary and the detection part vibrates greatly as a part of the vibration body of the detection vibration when the detection vibration is generated by the rotation. In the present embodiment, a three-leg tuning fork having three legs is used as a vibrating body, and among the three legs arranged side by side, the width of the rightmost leg 3 is 3/5 ± of the width of the other leg. 10%, that is, 3/5 · W2 · 0.9 ≦ W3 ≦ 3/5 · W2 · 1.1
Thus, a vibrating body that satisfies all of the above-mentioned desirable matters is provided.

The tripod tuning fork type vibrator used in the present embodiment has a plurality of natural vibration modes. Among these, the primary bending vibration of the three legs in the X direction, which is completed in the plane orthogonal to the thickness direction of the three-leg tuning fork shape, that is, the XY ′ plane, is the surface of the three-leg tuning fork 10. This is called internal vibration. The primary bending vibration of the three-leg tuning fork shape in the thickness direction, that is, the Z ′ direction of the three legs is referred to as out-of-plane vibration of the three-leg tuning fork 10. In a three-leg tuning fork, there are at least two out-of-plane vibrations that can be used for the gyro detection operation even if limited to the primary bending vibration.

  The first detected vibration of the tripod tuning fork 10 will be described with reference to FIG. FIG. 7 is a cross-sectional view of the leg as viewed from the Y ′ direction. In the out-of-plane vibration of the tripod tuning fork 10, the leg 1 and the pair of legs 3 and the leg 2 are bent out of the plane. This is a vibration mode for performing vibration. FIG. 7 shows the direction of displacement of each leg at a certain moment by an arrow. This vibration mode is referred to as first detection vibration.

  The second detected vibration of the tripod tuning fork 10 will be described with reference to FIG. FIG. 9 is a cross-sectional view of the leg as viewed from the Y ′ direction. In the out-of-plane vibration of the tripod tuning fork 10, the leg 2 and the pair of legs 3 and the leg 1 bend in the direction opposite to each other. This is a vibration mode for performing vibration. FIG. 9 shows the displacement direction of each leg at a certain moment by an arrow. This vibration mode is referred to as second detection vibration.

  Next, the drive vibration of the tripod tuning fork 10 will be described with reference to FIG. Among the in-plane vibrations of the three-leg tuning fork 10, there is a vibration mode in which the legs 1 and 2 perform in-plane vibrations that bend in directions opposite to each other while the legs 3 are stationary. FIG. 8 is a cross-sectional view of the leg viewed from the Y ′ direction, and the displacement direction of each leg at a certain moment is indicated by an arrow. This vibration mode is called drive vibration.

  Focusing on the arrangement of the legs 1 and 2 in the arrangement of each leg of the three-leg tuning fork 10, the legs 1 and 2 form an arrangement similar to a two-leg tuning fork, and the drive vibration is composed of the legs 1 and 2. It can be seen as in-plane vibration similar to the two-leg tuning fork. The in-plane vibration of the biped tuning fork is a self-contained vibrating body with the lower part of the base as a supporting part, but the driving vibration of the similar three-leg tuning fork 10 has almost no leakage of vibration to the supporting part. It has been confirmed.

  The reason why the leg 3 is stationary in the drive vibration is that the pair of legs 1 and 2 can realize self-contained vibration, but the width of the leg 3 is 3 with respect to the width of other legs. The resonance frequency in the X direction of the leg 3 is far from the resonance frequency of the in-plane vibration of the other leg and cannot be coupled to the vibration of the legs 1 and 2.

  In each out-of-plane vibration, the resonance frequency inherent to the leg is determined by the thickness t without being affected by the width of the leg, so that all three legs vibrate even if the width of the leg 3 is greatly changed. On the other hand, in the in-plane vibration, the driving vibration in which only the leg 3 is stationary is realized by changing the width of the leg 3 greatly. This is a major feature of the tripod tuning fork 10.

  Next, the relationship between the drive vibration and each detected vibration and the Coriolis force will be described. In the tripod tuning fork 10 that performs drive vibration, when the tripod tuning fork 10 is rotated at an angular velocity Ω around Y ′ at this time, the Coriolis force FC acts on the leg 1 that moves at the velocity VX in a direction orthogonal to the drive vibration. The Coriolis force -FC acts on the leg 2 moving at the speed -VX in the direction orthogonal to the drive vibration. That is, as shown in FIG. 7, the Coriolis forces FC and -FC act on the legs 1 and 2 of the tripod tuning fork 10 at the frequency of the drive vibration in the out-of-plane vibration direction. Accordingly, it can be seen that when the tripod tuning fork 10 in which the drive vibration is generated is rotated around the Y ′ axis at an angular velocity Ω, the detected vibration is excited by the Coriolis force through the movement of the legs 1 and 2. However, as shown in FIGS. 7 and 9, the movement directions of the legs 3 operating by the first detection vibration and the second detection vibration caused by the legs 1 and 2 using Coriolis force as the medium are the legs 1 and 2. The directions of movement are opposite to each other.

The output of the vibrating gyroscope is generated in the direction of the detected vibration orthogonal to the result of the Coriolis force FC = 2, M, Ω, and VX proportional to the speed acting on the drive vibration section that moves at high speed relative to the detected vibration system. This can be viewed as forced vibration due to the generated vibration force. When the drive vibration that vibrates at the natural frequency ω0 excites the detected vibration via the Coriolis force FC, the displacement of the drive vibration is a sine wave D · sinω0 · t of amplitude D, and the Coriolis force description formula FC = Since the Coriolis force generated in the detection direction from 2 · M · Ω · VX is 2M · Ω · D · ω0 · cosω0 · t, the vibration of the detection vibration system of the tripod tuning fork 10 having the natural frequency ω and the sharpness Q When the displacement of the part is expressed as Z (t) as a function of time and a differential equation is established, the following (Formula 1) is obtained.
M · d ² · Z (t) / dt ² + M · (ω / Q) · dZ (t) / dt + Mω ² · Z (t) = 2 · M · Ω · D · ω0 · cosω0 · t (Formula 1) )
The steady solution of this differential equation is a sine wave A · cos (ω0t−φ) having an amplitude proportional to the angular velocity Ω. Here, the amplitude A is A = 2 · D · Ω · (1 / ω0) · (ω / ω0) · ((1- (ω / ω0) ² ) ²
+ ((1 / Q) · (ω / ω0)) ² ) ^1/2 (Expression 2)
And the phase φ is
φ = arctan (Q · (ω0 / ω) − (ω / ω0)) ⁻¹ ) (Equation 3)
Where φ is a step-like function that changes to −90 degrees when ω0> ω and 90 degrees when ω0 <ω when Q is large.

  The phase φ indicates the phase relationship of the detected vibration with respect to the driving vibration, and the above equation (3) depends on whether the detected vibration frequency is higher or lower than the point where the detected vibration frequency matches the driving vibration frequency. Indicates a difference of 180 degrees. This indicates that the phase of the detected vibration excited by the Coriolis force by the drive vibration can be controlled by adjusting the frequency of the drive vibration with respect to the frequency of the detected vibration.

  The tripod tuning fork 10 used in this embodiment includes a first detection vibration having a resonance frequency ω = ω1 and a sharpness Q = Q1, and a second detection vibration having a resonance frequency ω = ω2 and a sharpness Q = Q2. The resonance frequency ω1 of the first detection vibration is larger than the resonance frequency ω2 of the second detection vibration, and ω1> ω2. The magnitude relationship between the values of the two resonance frequencies ω1 and ω2 cannot be changed unless the shape of the tripod tuning fork 10 is significantly changed, but the values of the two resonance frequencies ω1 and ω2 that are out-of-plane vibrations are in-plane. Since the resonance frequency ω0 that is vibration can be changed at the same ratio according to the thickness t of the plate, the magnitude relationship of the drive frequency ω0 with respect to the two resonance frequencies ω1 and ω2 is the thickness of the tripod tuning fork 10. It can be easily changed by changing t.

  In the present embodiment, the resonance frequency ω0 of the drive vibration is a value between the resonance frequencies ω1 and ω2 of the two detection vibrations. That is, by adjusting the thickness t, the magnitude relationship of ω1> ω0> ω2 is realized. In this relationship, as shown in FIG. 7 and FIG. 9, each detected vibration in which the driving vibrations are excited in opposite directions has a high resonance frequency of the first detected vibration when viewed from the drive vibration. Since the resonance frequency of the second detection vibration is low, the phase φ = φ1 when the driving vibration excites the first detection vibration and the phase φ = φ2 when the driving vibration excites the second detection vibration are mutually Considering the difference of 180 degrees, the direction of each detected vibration generated by the drive vibration due to the Coriolis force is the same, and the two detected vibrations strengthen each other.

When Q is large, Equation 2 can be approximately expressed as A = K · Ω / | ω−ω0 | with K as a proportional constant. In the case of the tripod tuning fork 10 in which the resonance frequency ω0 of the drive vibration is between the values of the resonance frequencies ω1 and ω2 of the two detection vibrations, A = K · Ω / | ω1-ω0 | + K · Ω / | ω0−ω2 That is, if the detuning degree of the first detected vibration is expressed as Δω1 = | ω1−ω0 |, and the detuning degree of the second detected vibration is expressed as Δω2 = | ω2−ω0 |, A = K · Ω / (1 / Δω1 + 1 / Δω2). FIG. 10 shows the magnitude of the amplitude A when the resonance frequency ω0 of the drive vibration is larger than the resonance frequency ω2 of the second detection vibration and smaller than the resonance frequency ω1 of the first detection vibration. As a sum of a one-dot broken line indicating the contribution of the second and a broken line indicating the contribution from the second detected vibration, a solid line is shown as a function of the frequency.

  As shown in FIG. 10, the sum of two hyperbolic curves, which are contributions from the first detection vibration and the second detection vibration, forms a pan bottom region 100 in a region between ω1 and ω2. This is because the amplitude is A = K · Ω / (1 / Δω1-1 / Δω2), and the resonance frequency ω0 of the drive vibration is larger than the resonance frequency ω1 of the first detection vibration, the detected vibration amplitude A is obtained. Compared with the region 200 showing a sharp amplitude change, the tripod tuning fork 10 in which the resonance frequency ω0 of the drive vibration is set in the region 100 of FIG. 10 detects the change in the degree of detuning adjusted by changing the resonance frequency of the drive vibration. This shows that it is possible to realize a characteristic in which the change in the vibration amplitude A is small and the Coriolis detection output hardly changes even if the degree of detuning is changed.

  Up to this point, the vibration body shape of the three-leg tuning fork 10 has been described only for the case where a strict restriction that the width of the detection leg is 3/5 ± 10% of the other leg has been described. It exists in all asymmetrical three-leg tuning forks in which the natural resonance frequency is changed with respect to other legs, and also exists in a symmetrical three-leg tuning fork. Therefore, also in general for a three-leg tuning fork, by setting the frequency ω0 of the drive vibration in the region between the first detection vibration and the second detection vibrations ω1 and ω2, the detuning degree described in the present embodiment. Therefore, it is possible to realize a characteristic in which the change in the output with respect to the change in is small and the detection output hardly changes depending on the degree of detuning.

  Next, an electrical drive detection method using an actual drive detection circuit will be described. FIG. 2 shows a cross section of the leg of the three-leg tuning fork 10 and cross sections of the electrodes 1L, 1R, 1U, 1D, 2L, 2R, 2U, 2D, 3U, 3D, and 3G.

  First, the case where the leg 2 performs in-plane vibration will be described. When the leg 2 is bent in the X direction, the vicinity of the electrode 2L extends in the Y ′ direction, and the vicinity of the electrode 2R contracts in the Y ′ direction. At this time, an electric field is generated in the −X direction near the electrode 2L inside the crystal due to the piezoelectric effect, and an electric field is generated near the electrode 2R in the X direction due to the piezoelectric effect. Due to these electric fields, the electrodes 2U and 2D have a higher potential than the electrodes 2L and 2R. Conversely, when a voltage is applied from the outside between the electrode 2L and the electrode 2U or 2D and a reverse voltage is applied from the outside between the electrode 2U or 2D and the electrode 2R, the piezoelectric effect is reversible. Inside, an electric field is generated in the −X direction near the electrode 2L, and an electric field is generated in the X direction near the electrode 2R. This electric field expands the vicinity of the electrode 2L of the leg 2 and contracts the vicinity of the electrode 2R. The leg 2 bends in the X direction. Therefore, the in-plane vibration can be oscillated using the leg 2 by amplifying the voltage generated in the electrode 2U or 2D by bending in the X direction, adjusting the phase, and applying this voltage to the electrodes 2L and 2R. .

  In the present embodiment, all the legs 1 and 2 that operate by driving vibration are driven. That is, considering the movement direction of the leg of the drive vibration shown in FIG. 8, the leg 1 applies voltages to the front and back electrodes 1U and 1D using the left and right electrodes 1L and 1R as reference voltages. Conversely, the voltage may be applied to the left and right electrodes 2L and 2R with reference to the voltages of the front and back electrodes 2U and 2D. In the present embodiment, the voltages from the electrodes 1L, 1R, 2U and 2D are input to the amplifier G, the output of the amplifier G is phase-shifted by the phase shift circuit P, and applied to the electrodes 1U, 1D, 2L and 2R. By doing so, the drive vibration is self-excited.

In this state, when the entire three-leg tuning fork 10 is rotated around the Z ′ axis at an angular velocity Ω, the three-leg tuning fork 10 has 2 as described above through the movement of the legs 1 and 2 of the three-leg tuning fork 10. Two detection vibrations are generated, and when there is no rotation, out-of-plane vibrations are generated in the leg 3 that is stationary. A case where the leg 3 vibrates out of plane will be described. When the leg 3 bends in the Z ′ direction, the vicinity of the electrode 3D contracts in the Y ′ direction. At this time, due to the piezoelectric effect, an electric field is generated in the X direction in the region where the electrode 3D of the leg 3 exists as viewed in the Z ′ direction. Accordingly, the electrode 3D is at a lower potential than the reference electrode 3G. At this time, the vicinity of the electrode 3U extends in the Y ′ direction. Due to the piezoelectric effect, an electric field is generated in the −X direction in the region where the electrode 3U of the leg 3 is present when viewed in the Z ′ direction. Therefore, the electrode 3U has a higher potential than the reference electrode 3G. On the other hand, when the leg 3 is bent in the −Z ′ direction, the region where the electrode 3D exists extends in the Y ′ direction. At this time, due to the piezoelectric effect, an electric field is generated in the −X direction in the region where the electrode exists. Accordingly, the electrode 3D has a higher potential than the reference electrode 3G. At this time, the vicinity of the electrode 3U contracts in the Y ′ direction. Due to the piezoelectric effect, an electric field is generated in the X direction in the region where the electrode 3U of the leg 3 is present as viewed in the Z ′ direction. Therefore, the electrode 3U is at a lower potential than the reference electrode 3G. That is, the detected vibration can be detected as voltages in opposite directions generated at the electrode 3U and the electrode 3D with reference to the potential of the reference electrode 3G of the leg 3. Of course, the voltage between the electrodes 3U and 3D may be directly measured without using the electrode 3G.

  The detection signal of the Coriolis force is generated by connecting the electrode 3G to the ground to generate a reference voltage, inputting the voltages of the electrodes 3U and 3D to the differential buffer D, leading to the multiplication circuit M via the differential buffer D, and The output of the amplifier G is shifted by 90 degrees by the phase shift circuit P2 and multiplied by the reference signal binarized by the comparator C for the purpose of correcting that the Coriolis force is delayed by 90 degrees. The result of detection by multiplication can be further smoothed by the integration circuit S and detected as an accurate DC output. Since this DC output is proportional to the Coriolis force, and the Coriolis force is proportional to the angular velocity Ω, the angular velocity Ω can be known from this DC output. Here, the reason why the differential detection is used for the detection is to improve the symmetry of the circuit and reduce the drift of the circuit system.

  The present invention can be applied to a gyro sensor using a tripod vibrator.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing the appearance of a tripod tuning fork type vibration gyro which is an embodiment of the present invention, and showing coordinates used for the following description. It is a schematic diagram which shows the cross section of the tripod tuning fork which is embodiment of this invention, and shows a circuit block and wiring. FIG. 3 is a surface view showing the appearance of a tripod tuning fork type vibrating gyroscope according to an embodiment of the present invention, showing coordinates used for the description, and showing a part of an electrode. 1 is a back view showing an appearance of a tripod tuning fork type vibration gyroscope according to an embodiment of the present invention, showing coordinates used in the following description, and showing a part of an electrode. It is a perspective view which shows the external appearance of the conventional tuning fork type crystal gyro, shows a coordinate, shows a part of electrode, and shows the rotation direction of an anisotropic crystal. It is the wiring cross section of the cross section of a leg and a drive detection circuit of the conventional tuning fork type crystal gyro. It is operation | movement explanatory drawing which shows the drive vibration of the tripod tuning fork type vibrating body which is embodiment of this invention. It is operation | movement explanatory drawing which shows the detection vibration of the tripod tuning fork type vibrating body which is embodiment of this invention. It is operation | movement explanatory drawing which shows the detection vibration of the tripod tuning fork type vibrating body which is embodiment of this invention. It is a figure showing the output of the tripod tuning fork type vibration gyroscope which is embodiment of this invention with respect to a frequency.

Explanation of symbols

1L, 1R, 1U, 1D Electrodes 2L, 2R, 2U, 2D Electrodes 3U, 3D, 3G Electrodes DR, SE Terminals S1, S2, GND Terminals 1-3 Leg 9 Base 10 Three-leg tuning-fork type vibration gyro 11 Support part A1 A3 Weights W1, W2, W3 Leg width U Groove width K Shoulder width C Comparator
D differential buffer G amplifier M multiplication circuit P, P2 phase shift circuit S integration circuit FC, -FC Coriolis force VX, -VX speed J1-J8 electrode J10 tuning fork type vibrator J11 first leg J12 second leg J15 base JC comparator
JD differential buffer JG amplifier JM multiplication circuit JP, JP2 phase shift circuit JS integration circuit

Claims (5)

A vibrator having three legs arranged at the base, an oscillating means for driving two of the three legs at a predetermined drive frequency, and another one different from the driven two legs Detecting means for detecting the Coriolis force by the legs of the three legs, the three legs being arranged in parallel in the same direction from the base with a predetermined distance from each other, and the oscillating means of the three legs Among them, the center leg and one leg adjacent to the center leg are driven, the other leg adjacent to the center leg is substantially stationary, and the detection means generates the Coriolis force generated on the other leg. In the vibration gyro to detect,
The vibrator has a first detection vibration mode having a first vibration frequency as a resonance point, and a second detection vibration mode having a second vibration frequency as a resonance point, and the driving frequency of the oscillation means. A vibration gyro characterized in that is a frequency between the first vibration frequency and the second vibration frequency.   2. The vibration of the first detection vibration mode and the vibration of the second detection vibration mode that are generated based on the Coriolis force act so that the other leg vibrates in the same phase. Vibration gyro.   The first detection vibration mode is a mode in which the one leg and the other leg vibrate in opposite phases to the center leg, and the second detection vibration mode is a mode in which the one leg and the center leg are 3. The vibration gyro according to claim 1, wherein the vibration gyro is in a mode that vibrates in an opposite phase to the other leg.   2. The vibrating gyroscope according to claim 1, wherein the width of the other leg is narrower than the width of the central leg and the width of the one leg.   The width of the one leg and the width of the center leg are substantially the same, and the width of the other leg is 3/5 ± 10% of the width of the one leg or the center leg, 2. The vibrating gyroscope according to claim 1, wherein a shoulder portion is provided at a portion connecting the one leg and the base portion.

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